• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.4
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• pp.273-282
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• 2023

Probabilistic safety assessment (PSA) has been widely used to evaluate the seismic risk of nuclear power plants (NPPs). However, studies on seismic PSA for process plants, such as gas plants, oil refineries, and chemical plants, have been scarce. This is because the major disasters to which these process plants are vulnerable include explosions, fires, and release (or dispersion) of toxic chemicals. However, seismic PSA is essential for the plants located in regions with significant earthquake risks. Seismic PSA entails probabilistic seismic hazard analysis (PSHA), event tree analysis (ETA), fault tree analysis (FTA), and fragility analysis for the structures and essential equipment items. Among those analyses, ETA can depict the accident sequence for core damage, which is the worst disaster and top event concerning NPPs. However, there is no general top event with regard to process plants. Therefore, PSA cannot be directly applied to process plants. Moreover, there is a paucity of studies on developing fragility curves for various equipment. This paper introduces PSA for gas plants based on FTA, which is then transformed into Bayesian network, that is, a probabilistic graph model that can aid risk-informed decision-making. Finally, the proposed method is applied to a gas plant, and several decision-making cases are demonstrated.

• Journal of the Korean Institute of Gas
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• v.9 no.4 s.29
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• pp.57-61
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• 2005

The objective of paper is to carry out a comparative Quantitative Risk Assessment (QRA) of two KOGAS tank designs using a fault tree methodology, a standard 'Full Containment' tank and a 'Membrane' tank. For the membrane tank, both the initial KOGAS design and 4 modified KOGAS designs have been assessed, giving six separate cases. In this paper, the frequencies of releases are quantified using a fault tree approach. For clarity in the analysis, and to ensure consistency, all cases have been quantified using the same fault tree. Logic within the fault tree is used to select each of the cases. Full quantification of risks is often difficult, owing to a lack of relevant failure data, but the aim of this study has been to be as quantitative as possible, with full transparency of failure information. The most significant general cause of external LNG leaks is predicted to be a seismic event, which has been quantified nominally. 4modified KOGAS desiens to Prevent damage of bottom membrane panels that was shown in preparatory estimation could quantitively confirm safety improvement. According to result, the predicted frequencies of an external LNG leak for the full containment and modified membrane tanks are very similar, failures due to dropped pumps are predicted to be significantly greater for the membrane tank with thickened plate than for the full containment tank.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.3-6
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• 2007

Korea Aerospce Research Institute(KARI) has been developing the first civilian rocket, Korea space launch vehicle (KSLV-I), which can put the small size satellite into designated orbit. Developing launch vehicles contains a lot of uncertainty due to large scale, complexity, and technical difficulty. The uncertainty may become risk in the areas of business and technology which causes schedule delay, cost increase, and design changes of subsystems and components. This study describes the technical risk identification methods using FTA and procedures of planning and implementation of risk assessment and reduction of launch vehicle propulsion system.

• Journal of the Korean Society of Safety
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• v.32 no.3
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• pp.160-171
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• 2017

US national research laboratories developed the first Vital Area Identification (VAI) method for the physical protection of nuclear power plants that is based on Event Tree Analysis (ETA) and Fault Tree Analysis (FTA) techniques in 1970s. Then, Korea Atomic Energy Research Institute proposed advanced VAI method that takes advantage of fire and flooding Probabilistic Safety Assessment (PSA) results. In this study, in order to minimize the burden and difficulty of VAI, (1) a set of streamlined VAI rules were developed, and (2) this set of rules was applied to PSA fault tree and event tree at the initial stage of VAI process. This new rule-based VAI method is explained, and its efficiency and correctness are demonstrated throughout this paper. This new rule-based VAI method drastically reduces problem size by (1) performing PSA event tree simplification by applying VAI rules to the PSA event tree, (2) calculating preliminary prevention sets with event tree headings, (3) converting the shortest preliminary prevention set into a sabotage fault tree, and (4) performing usual VAI procedure. Since this new rule-based VAI method drastically reduces VAI problem size, it provides very quick and economical VAI procedure. In spite of an extremely reduced sabotage fault tree, this method generates identical vital areas to those by traditional VAI method. It is strongly recommended that this new rule-based VAI method be applied to the physical protection of nuclear power plants and other complex safety-critical systems such as chemical and military systems.

• Journal of Institute of Control, Robotics and Systems
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• v.19 no.4
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• pp.328-333
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• 2013

Since a slight malfunction of control systems in a nuclear power plant may cause huge catastrophes, such control systems usually have multiple redundancy and reliable features, and their reliability and availability should be analyzed and verified thoroughly. This paper performed the reliability analysis of the SPLC (Safety Programmable Logic Controller) that is under developed as the control systems for the next generation nuclear power plant. One of the key features of SPLC is that it has multiple redundancy modes as faults happen, which means the reliability analysis for one fixed redundant model is not enough to analyze the reliability of SPLC. With considering this reconfigurable concept, FTA (Fault Tree Analysis) was used to capture fault-relationship among sub-modules. The analysis results show that MTTF (Mean Time to Fault) of SPLC is 45,080 hours, which is a about 4.5 times longer than the regulation, 10,000 hours.

• Journal of Environmental Impact Assessment
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• v.18 no.6
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• pp.359-366
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• 2009

CCS (Carbon Capture and Storage) is considered as the most promising interim solution to deal with the greenhouse gas such as $CO_2$ responsible for global warming. Even though carefully chosen geologic formations are known to contain stored gas for a long time period, there are potential risks of leakage. Up to now, applicable risk assessment procedures for the leakage of $CO_2$ are not available. This study presents a basis for risk analysis applicable to a complex geologic storage system. It starts with the classification of potential leakage pathways. Receptors and the leakage effect on them are identified and quantified. Then, a fault tree is constructed, which yields the minimum cut set (i.e., the most vulnerable leakage pathway) and quantifies the probability of the leakage risk through the cut set. The methodology will provide a tool for risk assessment in a CCS project. The outcomes of the assessment will not only ensure the safety of the CCS system but also offer a reliable and efficient monitoring plan.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.4
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• pp.27-33
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• 2013

In this study, the FMEA and FTA for reliability analysis of hybrid rocket motor are performed, that was designed in the Hybrid Rocket Propulsion Laboratory of Korea Aerospace University. In order to carry out these analyses the structure of the hybrid rocket motor is hierarchically divided into 36 parts down to the component level and FMEA is carried out with 72 failure modes. Reliability is assessed based on the FMEA, and the results are used in the FTA to evaluate the overall system reliability. In the FMEA, the relationship between the cause and failure modes, effects and their risk priorities are evaluated qualitatively. 27 failure modes are chosen as those with the critical severity that should be improved with priority. As a result of the FMEA / FTA study, a series of design or material changes are made for the improvement of reliability.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.105-106
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• 2008

전기철도에서 전차선은 차량에 직접 전력을 공급하는 설비로서 철도차량 운행 시 전차선의 사고를 예방하는 것은 매우 중요하다. 본 논문은 한국과 영국의 전기철도 전차선로의 안전성을 비교하기 위하여 영국의 전차선 안전성 분석 보고서와 한국의 전차선의 장애사례에 대한 데이터를 검토하였다. 분석한 데이터는 Fault Tree Analysis(FTA) 알고리즘에 적용하여 시스템의 신뢰도를 산정하는데 사용하였다. 이를 통해 전기철도 급전시스템의 사고율을 산정하여 각 요소별 및 전체 시스템의 신뢰도를 산정할 수 있었으며, 이는 유지보수주기 결정, 교체필요 요소의 결정 등에 활용될 수 있을 것으로 판단된다.

• Proceedings of the Korea Information Processing Society Conference
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• 2020.11a
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• pp.1097-1100
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• 2020

챗봇(Chatbot)은 자연어처리기술 등 인공지능 기술을 기반으로 한 사용자 친화적인 대화 방식 인터페이스를 제공하는 장점이 있어, 금융, 상담, 주문 등 다양한 산업 분야에서 적용되고 있다. 그러나, 챗봇의 응답이 사용자의 정신 모형과 불일치하는 경우, 다음 대화를 이어가는데 어려움을 야기하게 된다. 그러므로, 챗봇의 사용성을 확보하기 위해서는 응답 오류의 제거 또는 완화가 필수적이다. 기존의 챗봇의 사용성 개선과 관련된 연구들은 설문조사와 인터뷰 등 사용성 평가를 통해 상위 수준의 개선 방향만을 제안하고 있다. 따라서, 챗봇 개발 시, 실무자들이 응답 오류의 문제점을 분석하고, 이를 해결하기 위한 구체적인 개선 방안을 제시하는 데 한계가 있었다. 본 논문에서는 FMEA(Failure Modes and Effects Analysis) 기법을 활용해, 응답 오류의 치명도를 파악하고, 치명적인 오류들에 대해서는 FTA(Fault Tree Analysis) 기법을 기반으로 원인 분석을 실시하여 구체적으로 문제를 해결하기 위한 프로세스를 제안한다. 본 프로세스의 효용성을 검증하기 위해 주문 도메인의 챗봇에 적용해 보았다.

• Journal of the Korean Institute of Gas
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• v.1 no.1
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• pp.81-86
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• 1997

This study is to estimate the possibility of accident in chemical plants from the analysis of system component which affects the occurrence of top event. Among the various risk assessment techniques, the Fault Tree Analysis which approaches deductively on the route of accident development was used in this study. By gate-by-gate method and minimal cut set, the qualitative and quantitative risk assessment for hazards in plants was performed. The probability of occurrence and frequency of top event was calculated from failure or reliability data of system components at stage of the quantitative risk assessment. In conclusion, the probability of accident was estimated according to logic pattern based on the Fault Tree Analysis. And the failure path which mostly influences on the occurrence of top event was found from Importance Analysis.